Saturday, January 05, 2008

Do students of evolutionary biology appreciate the importance of random processes?

I've been teaching introductory human evolution type courses for three years now, so I found this paper in PLoS Biology pretty interesting. Basically, what they find is that student who are learning molecular biology and evolutionary biology have a hard time grasping the concept of randomness. Since I give a lot of short answer questions on my student's tests, I have some insight into how students think, and I agree with what they find. I've found that students tend to think that there's some intention or purpose that underlies evolutionary change... that organisms are actively moving to some goal. I like how they explain it in the excerpts I've put below.

here is what they find with respect to how students under-appreciate the importance of random processes:

"A common observation, which echoes the finding of Lecoutre et al., was that students were unwilling to see random processes as capable of directed effect in themselves—they routinely seek alternative rational explanations, the dominant one being the presumption of drivers that are actually responsible for the observed effects. In the absence of these drivers, for example, concentration gradients with respect to diffusion or active selection with respect to changes in allele frequency, the macroscopic behavior stops. The concept of random processes giving rise to emergent behavior is almost totally absent from their (explicit) thought processes.

...Given that much of evolutionary change is ultimately driven by, or is the result of, random processes rather than selection acting alone (see [5] and references therein), and given the apparent tendency of students to reject or overlook random events as the cause of emergent behaviors, what emerges is “neo-vitalist” mindset that presumes the presence of directed processes and imposes a level of meaning on the system (and its components) that may well not be present. Not all genetic changes have an immediate adaptive significance, and not all molecular processes are actively directed. Does this view interfere with understanding? The answer must be yes—since it leads one to assign purpose to a process (be it evolution or osmosis), and ignores what can be achieved at the underlying molecular level. From an evolutionary perspective, it leads to “just-so” stories that project meaning onto every variation, whether meaningful or not, and obscures the basic mechanisms that make evolutionary theory so valuable. On the molecular biology level it leads to anthropomorphic explanations of molecular interactions, some of which even imply action at a distance; e.g., ATP synthase molecules “seek out and grab” ADP molecules [25]."

and then, there's some discussion about what can be done to circumvent this problem:

"What, if anything, can be done to improve understanding of the role of random processes in particular, and emergent behaviors in general? Here are some hints. From the perspective of course and curriculum content, we need to provide students with opportunities to work with random systems, and explicitly state (and confront) their assumptions. One approach is through direct experimentation and accessible simulations that focus on the concept of randomness in specific processes. Under these conditions, events like allele loss from a population can be viewed as either the result of selection or genetic drift (or both)—leading to an understanding of the effects of population size on evolutionary effects. In the context of cell biology, students need to directly and explicitly consider the efficacy of diffusion in cellular and organismic context—why is it (apparently) adequate within a bacterial cell, but inadequate for a neuron? For a particular context, one might require students to predict, explaining their thinking, when a process is likely to be active (energy requiring) or passive (diffusive). How can the diffusive properties of a molecule be regulated by intracellular/extracellular structures and molecular interactions? For example, one could ask in which developmental or organismic contexts we can expect diffusion to be adequate (consider [4]). The development of experimental scenarios and/or computer-based simulations can then be used to test and re-evaluate students' assumptions."